1. Technical Field
The present invention relates to an acoustic wave device mainly used for mobile communication devices and the like.
2. Background Art
In recent years, acoustic wave devices provided with a plurality of high-frequency filters of different passbands have become more widely used in mobile telephones and the like.
FIG. 10 is a circuit diagram of conventional acoustic wave device 100.
Referring to FIG. 10, acoustic wave device 100 is provided with unbalance-balance conversion type low-frequency side filter 2 and unbalance-balance conversion type high-frequency side filter 3 that are disposed on piezoelectric substrate 1 made of piezoelectric single crystals. Low-frequency side filter 2 has a passband whose center frequency is relatively low. High-frequency side filter 3 has a passband whose center frequency is relatively high. Low-frequency side filter 2 and high-frequency side filter 3 are each configured such that longitudinally-coupled acoustic wave resonator 6 and one-terminal pair acoustic wave resonator 7 are connected in series between unbalanced terminal 4 and balanced terminal 5. Different electronic circuits are connected to balanced terminal 5 connected to low-frequency side filter 2 and balanced terminal 5 connected to high-frequency side filter 3, respectively, of acoustic wave device 100. Acoustic wave device 100 performs filtering of a plurality of electrical signals of different frequency bands.
Here, as the information on prior art document relating to conventional acoustic wave device 100, International Application Publication No. WO2008/096514 is known, for example.
With communication devices using conventional acoustic wave device 100 as described above, there is a tendency to downsize and reduce costs by sharing the electronic circuits connected to balanced terminals 5. For example, sharing balanced terminal 5 connected to low-frequency side filter 2 and balanced terminal 5 connected to high-frequency side filter 3 has been requested.
If balanced terminals 5 are shared in conventional acoustic wave device 100, low-frequency side filter 2 and high-frequency side filter 3 are connected via balanced terminal 5. Accordingly, low-frequency side filter 2 and high-frequency side filter 3 on a side of balanced terminal 5 are affected by impedance from each other, and isolation between the filters deteriorates. In addition, an insertion loss increases due to impedance mismatching between low-frequency side filter 2 and high-frequency side filter 3, and thus a magnitude of balance decreases. As a result, electrical characteristics of acoustic wave device 100 deteriorate.